Papermaking



Patented June 27, 1944 PAPERR 1 r John C. Sherman, fittieboro,Mass.,assigrior to A. P. W. Paper $0., L na, Albany, N. Y. a cor=poration of New York:

No Drawing. Application January 10, 19%,;

Serial No. 813,206

2 Claims. (oi. ite -s) tough, water-resistant protective membranes asfor the sheathing of buildings, the wrapping of goods, the lining ofshipping cases and forms for cement-pouring in the construction ofbuildings. Other well-known applications are for agricultural uses as inthe protection of crops and produce, and wherever structures or goodshave to be protected from climatic exposure. Such papers are used uponfreshly laid concrete or cement highway-lanes to ensure slow andsuitable curing, and in the facing of excavations and the like.

Such papers are commonly formed of two sheets of kraft or other suitablepaper adhered together with an intermediate film of asphalt or the like,or with pastes or glue suitably conditioned for the purpose.

That face of each sheet which is affected by the asphalt (hereinaftercalled the inner face) is combined with the inner face of its matedsheet through the adhesive quality of the asphalt (or the like)employed, the combining process usually being hastened and madeeffective by hot pressure.

In the production of such 'plied papers, it is.

customary to use for the two plies a sized paper, the sizing servingboth to toughen the paper and to prevent the absorption of so muchasphalt (e. g.) as would become objectionable through bleeding orthorough permeation of the paper with the i-mpregnant to a point whereatthe outer faces of the sheets 'woul'd themselves become tacky, difficultto roll up and'to handle.

The said impregnant is therefore not commonly used in amounts adequateto ensure the stout bonding together of the papers.

The adhesive film is commonly tenuous and discontinuous in spots, withresulting penetration of water or water-vapor ihto the interior of theplied material.

In many instances such papers, at the moment when their inner faces areto be pressed together, as above, receive between them a deposit ofcoarse open-meshed fabric, or a network or other system of textile cordsor yarns as of jute or cotton, or of raw strands of natural vegetablefibre simulating theresult to he obtained Wit more organized textileinserts.

When such papers are so combined, with intermediate .reenforcingmaterial, the presence of such material still further militates againstthe 'ilrm and continuous bonding of the two sheets.

Especially when strands of some natural fibre are so used, astheintermediate re-enforcing element, such strands, being relativelyincompressible and intractable in the application of them to thecomposite sheet, createalong each such fibre a potential zone ofdeficient waterprcofness. Such zones, each of threaddike fineness buthigh capillarity, readily accept vapor passed to them through theimperfectly coated sheets. Such vapor, condensed, remains and continuesto reduce the effectiveness of the adhesive bond, the fibres themselvesreacting to this condition by being rapidly disintegrated.

To offset in part such objectionable effects, it has been proposed toadd to such plied composites an intermediate film of a highly bibulouspaper or other sheet, which said sheet is, before or during the finalcombining process, heavily impregnated as with asphalt. When a three-plyconstruction is thus produced, a more effective barrier against waterand/or vapor is provided. The bibulous sheet receives the textilematerial more or less within its soft and yielding structure, and thelarger amount of asphalt used with it improves the general bondingeffect, despite the reluctance of the. sized outer sheets to accept asuflicient quota of asphalt.

However, the penetration of vapor through these outer sheets is not thusprevented, and the textile materials and the bibulous film itself becomemoist; and, when a moist condition is prolonged or intermitted butinterminably repeated, the deterioration of the material ensues, since,in a wet state, the elements of construction are deficient in strength.

However, the, inclusion of this intermediate bibulous film has greatutility, while dry, for these following reasons: (a) the film itself,after impregnation, followed by the consolidating effect of thatpressure which is used to compress the composite material, materiallyadds to the tear and tensile strengths or the composite; (b)

the "bond? between the ou'ter sheets is greatly facilitated, so that thecomposite material in use has less tendency to wrinkle, or to blisterfrom atmospheric water and/or vapor; (c) the bibulous film makes withthe reenforcing textile material so good a bond that the textilematerial is more adequately kept in place against the disthe rapiddeterioration of the bibulous film along with the outer plies fromwetness, as, notwithstanding its partial protection from asphalt, itremains to a degree hydrophilic, a result which follows from its natureand the inability of the mill process described above to give it to anentirely effective waterproofness.

I have found it practicable to build up a bibulous film having unusuallyhigh Mullen and tensile strength when wet, as by suitable treatment withimpregnants combined with taming or other setting factors which conservethe original quality of the film to a marked, degree when wet, withoutmaterially diminishing its acceptance of molten asphalt or otherwater-proofing saturant.

A composite material therefore, as produced under this invention, mayhave either of two final forms. (First) it may comprise two externalsheets of the usual sized paper each of which has been treated on and inits inner face with asphalt, and an intermediate film of wetstrengthenedpaper-like material; all being bonded as by hot pressure. (Second) itmay comprise two external sheets as above, treated as stated, a centralwet-strengthened film as above, and-intermediate between said film andsaid sheets-it may have a deposit of textile material in woven, knitted,netted or more or less random formation, said deposit being made uponeither one or both faces 0! said film.

There is a third form of construction one may make without departingfrom the scope of this invention, consisting in wet-strengthening boththe intermediate bibulous film and either one or both of the externalpaper sheets, such sheets for external use to be given thewet-strengthening treatment before they are resin-sized in theconventional tub-sizing way.

Means for imparting to a thin, bibulous film of paper-making material ahigh degree 0! mechanical strength when wet are to some extent knowntoday and may be used in carrying out this invention.

Among such means are the treatment of the said film, prior to itsinclusion in the composite structure of my invention, with a bath ofwater containing appropriate mixtures of glue and a chemical such asformaldehyde which strengthens the glue against weakness from wetting;also, alternatively, one may use a bath of the fiuid components of asynthetic resin, such as a resin described in U. 8. Patent #2,111,698 ofMarch 22, 1938, to Siefert and Stadler on the process of preparinghydrophobic cellulose fibrewhere by is meant each individualizedfibre-provided suillcient resinous bath is used to affect theinterfibrous voids in the sheet formed with such resinous content. Or asomewhat equivalent protection can be given by a bath of dextrin withits appropriate fixatives; '01 the requisite wet strength may beobtained by the wet-strengthening of the pulp by above means in thebeater or before it is converted into paper.

Any of these or other methods of immunizing a cellulosic fibre againstthe eilects of wetness may be used in my invention without departingfrom my invention. Also,\ the bibulous film itself along with the papersheets which form the outer plies of my structure, may be individuallyor together given a wet-strength as by any of'the above or other means.

Such treatment must be given to each individual ply-that is, to thebibulous film and to the paper sheets of the outer plies-if suchtreatment precedesthe combining process whereby the said film and thesaid sheets, along with whatever reenforcing strands or the like-if anyare used, are combined,

This would be the usual practice in that instance where a non-aqueouscementltious binder is used--such as asphaltto combine the pliedstructure. But in other instances, wherein the binder is sumcientlyhydrophylic, the wetstrengthening treatment of my central ply or of allplies, may take place coincidently with the plying operation andsubsequent drying processes.

To those skilled in the arts of sizing and otherwise impregnatingcellulosic fibres and fibrous films and sheets, it will be obvious thatall oi the above noted methods of wet-strengthening have.

as their common characteristic that they do not, if properly used,produce a sheet which is thereafter incapable of receiving eitheraqueous or non-aqueous impregnants and bonding or cementing agents, butthat they serve to afiect all adjacent individual fibres by a bonditself immune to destruction from wetness.

Thus, for example, it I apply to a bibulous (so-called "water-leaf")film of reasonably uncompacted structure-(say of a density, according tothe accepted scale of paper densities, of from 30 to 75) atreatment; asby tub-dipping or by kissing-rolls, with glue and formaldehyde in water,and thereafter dry the film so treated, it remains stout when wet, butis relatively unaflected so far as concerns its subsequent treatmentwith asphalt in a molten state or ina water-dispersed or colloidal" oremulsified fluid form, or by other acceptable impregnants, such asstarch, starch or dextrine with fi atives included, case-in glue, or anyoi the usual synthetic resins in their fluent form.

As an instance, I have treated a water-leaf sheet of a mixed furnish ofsulphite and groundwood with a bath of glue and formaldehyde so preparedas to add to grams-weight of said sheet, air dry, an added weight ofimpregnants of about 5% air dry, up to 10%, according to the strength ofthe glue so used, and have thereafter This result is taken as typicalthough in practice, to bring the sheets so tested within thescalereading of my Mullen machine, I have had to insert into the Mullenmachine four piles of the dry and four plies of the wet sheet forcomparison; scale readings being for such tests: 16 points for the dryand 40 points for the wet sheets.

The period of preliminary immersion in water for the wet test was tenseconds, but I have found no material reduction of wet Mullen afterprolonged water-soaking.

The absorptivity of the treated sheets for subsequent impregnation isbroadly noted in a typical test as follows:

Comparison of treated and untreated paper Water absorbed Grams 100 gramsair dry water-leaf sheet before treatment 300 105 grams, of same stock(100 grams pulp grams of impregnant) 250 Weight of absorbed water wasfigured by prolonged immersion of both types of sheet in water,

then hanging up to dry until dripping substantially stopped, and thenweighing.

It will be clear to those skilled in the art relative hereto, that,especially with the glue-formaldehyde treatment, I have set up withinthe gross structure of the paper a sort of synthetic resin.

The glue-formaldehyde mixture, after being dried in bulk, sets up as ahorny material similar to the known resins.

But in the minimal amounts of such resin which I form as above and applyto paper, this formation of horn-like product is not materiallyefiective to alter the ordinary characteristics of the paper.

Thus the water-crawl is not markedly affected, flexibility remainssatisfactory, and the dry-strength of the sheet not materially changedsince I have avoided subsequent subjection of the sheet to such heavypressure as is usual in the sizing of ordinary paper.

This method of impregnation is commonly believed, as my tests confirm,to serve mostly as a means of attaching individual cellulose fibres orshreds of fibre to one another, ile leaving the gross structure of thesheet not markedly affected adversely to subsequent impregnation.

The cementitious union of adjacent contacting fibres effected by thetreatment does, however, serve, (as indicated by the tabulation above)to prevent the dislocation of such fibres when stressed in awater-soaked condition.

It is, therefore, evident that the film of paper V treated for use in myinvention does not revert to a. wet-pulpous condition when subjected. toseepage of water in.the plied structures which Iproduce.

If, in the further application of my invention, it is desired to renderall the plies, or the outer plies alone, or one of them, immune toinjury from wetness, the sheet for which such application is to be madeshould be run off without heavy sizing of the conventionalsaponified-resin type or the like.

It should be treated in its bibulous form with any of my statedimpregnants, such as the glue formaldehyde mixture, applied in atub-sized system or by a kissingroll, to the necessary degree toimmunize it to water.

Thereafter it may be tub-sized with the conventional sizings to give itstiffness, superficial water-resistance, and the familiarcharacteristics of a normally-sized sheet.

Such sizing, as resin-sizing, is not desired for the central ply forwhich the highest possible residual absorptivity for impregnants such asasphalt is desired.

For the outer sheet or plies, often for uses where exposure to theweather is an incident of use, the normal characteristics of a sheet forsuch exposure, as with a resin size, are desirable.

These outer sheets, especially the sheet for exposure to weather as insheathing or wallcovering paper, may indeed shrink away from whateverfastening means are used to hold them in place, and thus become crackedor ruptured either along the confining means or at some intermediateplace.

In this case, the efficacy of my central ply,

treated as described, now becomes important as a means of protecting theplied material from final disintegration.

The central ply, with its coatings 'of asphalt or other ply-cementingagency, is in itself effective to cement the outer sheet in place,despite localized lines of rupture, and in itself it resists the furtherdevelopment of weakness in the plied structure under wet conditions ofuse.

Having thus described my invention without limitation to the specificsteps enumerated or to the limited fields of application enumerated, Iclaim:

1. A composite paper comprising outer sheets of Kraft paper, anintermediate film of bibulous wet-strengthened paper, said sheets beingabsorptive to asphalt, and asphalt films between said sheets and saidfilm of bibulous wet-strengthened paper bondingthem together.

2. A composite sheet comprising outer sheets of Kraft paper, a centrallydisposed sheet of bibulous wet-strengthened paper, a deposit of textilestrands disposed upon the central sheet, said sheet and textile strandsbeing absorptive to asphalt, and a film of asphalt between the adjacentfaces of, the sheets and embedding the textile strands and bonding thesheets and strands together.

JOHN C. SHERMAN.

